1. Field of the Invention
This invention relates to an optical device, more particularly to an optical device for panoramic viewing.
2. Description of the Related Art
Various methods of forming an image of a panoramic scene at a receptive area are well known, for example, a single wide-angle lens can be used. However, in such an arrangement, as the viewing angle increases the various aberrations increase rapidly and the illumination decreases considerably as a result of reflection losses. This disadvantage can be overcome by using a plurality of lenses, each covering a particular sector of the panoramic view. An arrangement of this kind is disclosed in British Patent No. GB 1286565 and an alternative arrangement is disclosed in German Patent No. DE 2926731.
The multi-lens arrangements described in these specifications are not suitable for viewing through a small window, as may be necessary for example in an aircraft, where disturbance to its surface must be minimal. Furthermore, the known arrangements are designed to operate with one continuous receptive area. This is unnecessary when photodetectors are used, and is particularly undesirable when cooled solid state infra-red detector arrays are used as each array requires extra room for the cooling means.
It is therefore an object of the present to alleviate the aforementioned disadvantages.